1. Field of the Invention
Embodiments of the disclosure relate to a method and a device for processing touch information, and more particularly, to a method and a device for processing touch information capable of effectively removing a high frequency noise included in touch sensor data and a flat panel display using the method and the device.
2. Discussion of the Related Art
Examples of a flat panel display include a liquid crystal display (LCD), a plasma display panel (PDP), a field emission display (FED), and an organic light emitting diode (OLED) display. Most of them have been put to practical use in electric home appliances or personal digital appliances and have been put on the market.
With a recent trend toward a thin profile and lightness in weight of electric home appliances or personal digital appliances, a button switch as the user's input means has been substituted for a touch sensor. Examples of the touch sensor include a capacitive touch sensor, a resistance touch sensor, a pressure touch sensor, an optical touch sensor, and an ultrasonic touch sensor, etc. One kind of an optical touch sensor that has been widely used is an in-cell touch panel type touch sensor in which touch sensors are formed inside a pixel of a display device.
The in-cell touch panel type touch sensor, as shown in FIG. 1, includes a sensor thin film transistor (TFT) differently generating a light current “i” depending on a touch or non-touch operation, a sensor capacitor Cst storing charges resulting from the light current “i”, and a switch TFT outputting the charges stored in the sensor capacitor Cst. In the in-cell touch panel type touch sensor, light sensing data generated in the touch operation is different from light sensing data generated in the non-touch operation. A flat panel display can detect information about a touch position of a user's finger or a touch pen based on the light sensing data of the in-cell touch panel type touch sensor.
The optical touch sensor has a problem that the light sensing data is greatly affected by an external illuminance or a shadow. To solve the problem, an optical black method and a reference image difference method have been proposed. However, the optical black method cannot remove a specific deviation of a display panel, and the reference image difference method recognizes an image on a display screen or an image reflected by a polarizing plate as a basic receiving light pattern. Accordingly, a frame difference method has been recently proposed to solve the problem.
In the frame difference method, light sensing frame data input in a previous frame is subtracted from light sensing frame data input in a current frame to generate new difference data. Then, a meaning touch boundary portion is calculated using a determined threshold value as a parameter. In the frame difference method, a noise component included commonly in the light sensing frame data is removed in the same manner as a differential amplifier. The frame difference method, as shown in FIG. 2, employs the fact that when a user touches a display screen with his or her finger, his/her finger inevitably moves slightly on XY-plane. In the frame difference method, a charge amount of a movement of his/her finger indicated by a notch portion can be detected based on the fact.
However, in the case of using the related art frame difference method, in theory, a noise existing between adjacent frames has to be completely removed. However, as can be readily seen from FIGS. 3 and 4, a high frequency noise that is not perceived by his or her eye is scattered in several positions. FIGS. 3 and 4 illustrate binary images for detecting a high frequency noise that is not perceived by his or her eye. More specifically, in the binary image shown in FIG. 3, a portion in which a value of difference data between two adjacent frames is equal to or greater than “1” (minimum data unit) is indicated in a black, and a portion in which a value of difference data between two adjacent frames is zero is indicated in a white. In the binary image shown in FIG. 4, a portion in which a value of difference data between two adjacent frames is equal to or greater than “2”, “3”, . . . , “9” respectively is indicated in a black, and a portion in which a value of difference data between two adjacent frames is less than “2”, “3”, . . . , “9” respectively is indicated in a white.
The related art frame difference method uses an uppermost portion of a finger boundary portion as touch coordinates using the determined threshold value. However, it is difficult to distinguish the finger boundary portion from the high frequency noise. Therefore, a portion that is not touched with his/her finger may be detected as touch coordinates. Further, the high frequency noise may be removed using a touch sensor integrate circuit (IC) including the differential amplifier through a physical or hardware method, but a large number of transistors are necessary. As a result, the manufacturing cost, the size, and the weight of the flat panel display increase.